1. Field of the Invention
The present invention relates to an internal combustion engine provided with centrifugal decompressing mechanisms for reducing compression pressure to facilitate starting the internal combustion engine by opening a valve included in the internal combustion engine during the compression stroke in starting the internal combustion engine.
2. Description of the Related Art
An internal combustion engine provided with centrifugal decompressing mechanisms each including a flyweight is disclosed in JP2001-221023A. A decompression lever included in this prior art decompressing mechanism is integrally provided with a flyweight and a decompression cam. There is formed a round hole of a diameter slightly greater than that of a pin fixedly pressed in a camshaft in a position perpendicular to the axis of the camshaft. The decompression lever is supported by the pin inserted in the round hole for turning on the camshaft.
Assembling the decompression lever provided with the flyweight of the prior art decompressing mechanism and the camshaft requires troublesome work for pressing the pin in the hole formed in the camshaft. Assembling facility may be improved by fitting the pin in the hole of the camshaft in a running fit.
Since the pin inserted in the hole of the flyweight supports the flyweight for turning thereon, there is a small clearance between the pin and the flyweight and, if the pin is inserted in the hole of the camshaft in a running fit, there is also a small clearance between the pin and the camshaft. Consequently, the flyweight and the pin are liable to move relative to each other in directions parallel to the axis of turning of the flyweight and in directions of turning of the flyweight, and the flyweight located at a decompression withholding position is caused to move relative to and strike against the pin by the vibrations of the internal combustion engine, which is liable to generate rattling noise.
The present invention has been made in view of the foregoing problems and it is therefore an object of the present invention to restrain the flyweight of a decompressing mechanism from movement relative to a pin supporting the flyweight for turning thereon, and to prevent or control the generation of rattling noise. Another object of the present invention is to reduce the clearance between the pin and the flyweight to substantially null to prevent or control the generation of rattling noise.
According to the present invention, an internal combustion engine comprises: a crankshaft; a camshaft driven for rotation in synchronism with the crankshaft; an engine valve controlled for opening and closing by a valve-operating cam; and a decompressing mechanism for opening the engine valve during a compression stroke in a starting phase; wherein the decompressing mechanism (D) includes: a pin supported so as to be turnable on the camshaft; a flyweight supported for turning relative to the camshaft by the pin on the camshaft; and a decompression cam capable of operating together with the flyweight to apply valve opening force to the engine valve; the pin is inserted in holes formed in the flyweight so as to be turnable; and a restraint is provided to restrain the pin and the flyweight from movement relative to each other.
In this internal combustion engine, facility of mounting the flyweight on the camshaft is improved because the pin is able to turn relative to the camshaft, and the collision of the flyweight and the pin against each other due to vibrations of the internal combustion engine is prevented or controlled because the flyweight and the pin are restrained from movement relative to each other.
Thus, the present invention has the following effects. Since the pin supporting the flyweight of the decompressing mechanism is supported so as to be turnable on the camshaft, facility of mounting the flyweight on the camshaft is improved. Since the pin and the flyweight are interlocked by the restraining means capable of restraining the pin and the flyweight from movement relative to each other, generation of rattling noise due to the collision of the pin and the flyweight against each other due to the vibrations of the internal combustion engine can be prevented or controlled.
The restraint may restrain the pin and the flyweight from movement relative to each other in directions parallel to the axis of turning of the flyweight swings.
The restraint which restrains the pin and the flyweight from movement relative to each other in directions parallel to the axis of turning of the flyweight may include an elastic member placed between the pin and the flyweight and capable of applying resilient force to the pin and the flyweight.
Frictional forces due to the resilient force of the elastic member acting between the elastic member and the pin, between the elastic member and the flyweight and between the flyweight and the pin, restrain the flyweight and the pin from movement and turning relative to each other.
The restraint which restrains the pin and the flyweight from movement relative to each other in directions parallel to the axis of turning of the flyweight may include a first connecting part formed in one of the pin and the flyweight; and a second connecting part formed in the other of the flyweight and the pin for engaging with the first connecting part, the first connecting part has a first taper part, and the second connecting part has a second taper part formed in a shape conforming to that of the first taper part through plastic deformation of a part of one of the flyweight and the pin after the pin has been inserted in the holes.
Since the second taper part is formed through copying plastic deformation so as to conform to the first taper part after the pin has been inserted in the holes and the flyweight has been temporarily mounted on the pin, the deviation of the degree of plastic deformation can be easily absorbed by the taper parts of the connecting parts. Thus, the gap between the pin and the flyweight with respect to directions parallel to the axis of turning can be diminished substantially to null by a simple method that processes the flyweight or the pin for plastic deformation and the pin and the flyweight are restrained accurately from movement relative to each other in directions parallel to the axis of turning.
The restraint may restrain the pin and the flyweight from movement relative to each other in turning directions of turning of the flyweight. Thus, the pin and the flyweight are restrained from movement relative to each other in the turning directions.
The restraint which restrains the pin and the flyweight from movement relative to each other in the turning directions may include a first connecting part formed in one of the pin and the flyweight and a second connecting part formed in the other of the flyweight and the pin for engaging with the first connecting part, and the first and the second connecting parts may be provided with first and second detaining parts, respectively. The restraint including the first and the second connecting parts provided with the detaining parts restrains the pin and the flyweight from movement relative to each other in the turning directions. The first and the second detaining parts of the restraint which restrains the pin and the flyweight from movement relative to each other in the turning directions may have non-circular shapes, respectively, as viewed along the axis of turning of the flyweight.
In the restraint which restrains the pin and the flyweight from movement relative to each other in the turning directions, the first connecting part may have a first taper part and a first detaining part, and the second connecting part may have a second taper part and a second detaining part formed through the plastic deformation of a part of one of the flyweight and the pin so that the second taper part and the second detaining part conform to the first taper part and the first detaining part, respectively, after inserting the pin in the holes.
Thus, the deviation of the degree of plastic deformation can be easily absorbed by the taper parts of the connecting parts. Therefore, the gap between the pin and the flyweight with respect to directions parallel to the axis of turning and the gap between the pin and the flyweight with respect to the turning directions of the flyweight can be diminished substantially to null.
Consequently, the deviation of the degree of plastic deformation can be easily absorbed by the taper parts of the connecting parts. The gap between the pin and the flyweight with respect to directions parallel to the axis of turning can be diminished substantially to null by a simple method that processes the flyweight or the pin for plastic deformation and the pin and the flyweight are restrained accurately from movement relative to each other in directions parallel to the axis of turning and the turning directions.
The internal combustion engine may be provided with both the restraint which restrains the pin and the flyweight from movement relative to each other in directions parallel to the turning axis of the flyweight and the restraint which restrains the pin and the flyweight from movement relative to each other in the turning directions. Thus, the pin and the flyweight can be surely restrained from movement relative to each other.